1. Field of the Invention
The present invention relates to a learning device that learns values of multiple parameters included in a model formula expressing a detected waveform of a sensor with a mathematical expression and to a fuel injection system having the learning device.
2. Description of Related Art
In order to accurately control output torque and an emission state of an internal combustion engine, it is important to accurately control an injection mode of fuel injected from an injector such as injection quantity and injection start timing of the fuel. Therefore, conventionally there has been proposed a technology that senses the actual injection mode by sensing fuel pressure, which fluctuates with the injection.
For example, the technology detects the actual injection start timing by detecting timing when the fuel pressure starts decreasing due to the injection and senses decrease in the fuel pressure caused with the injection to sense the actual injection quantity. If the actual injection mode can be sensed in this way, the injection mode can be controlled accurately based on the sensing value.
When the fluctuation of the fuel pressure is sensed, a fuel pressure sensor (a rail pressure sensor) directly provided to a common rail (a pressure accumulator) cannot sense the fuel pressure fluctuation correctly because the fuel pressure fluctuation caused with the injection is damped inside the common rail. Therefore, according to an invention described in Patent document 1 (JP-A-2000-265892), a fuel pressure sensor is provided to a high-pressure pipe at a connection between the high-pressure pipe and the common rail. The fuel is supplied from the common rail to the injector through the high-pressure pipe. Thus, the invention aims to sense the fuel pressure fluctuation caused with the injection before the fuel pressure fluctuation is damped in the common rail.
A following point should be taken into account when multiple injection (multi-stage injection) for performing fuel injection multiple times per combustion cycle is performed. That is, in the waveform detected with the fuel pressure sensor, a portion of the detected waveform (refer to part (b) of FIG. 7) corresponding to n-th injection is overlapped with a waveform component (refer to part (b) of FIG. 8) resulting from m-th injection preceding the n-th injection. In the example of FIG. 7, m=n−1. In FIGS. 7 and 8, I indicates drive current of the injector and P is the fuel pressure.
Therefore, the inventor of the present invention studied a scheme of extracting the waveform component resulting from the n-th injection by subtracting the waveform component resulting from the m-th injection from the waveform detected with the fuel pressure sensor, thereby sensing the actual injection mode based on the extracted waveform component. More specifically, a model formula expressing the m-th injection waveform component with a mathematical expression is stored beforehand, and a model waveform expressed with the model formula is subtracted from the detected waveform detected with the fuel pressure sensor.
Furthermore, the inventor studied a scheme of learning values of multiple parameters included in the model formula to approximate the model waveform to the actual waveform. More specifically, the values in the entire existence ranges of the parameters are sequentially assigned to the model formula, and the combination of the parameter values that approximates the model waveform to the actual waveform most is calculated. The parameter values calculated in this way are stored as learning values, thereby updating the parameter values.
However, if it is attempted to perform the calculation by assigning the values in the entire existence ranges of all the parameters to the model formula in this way, the number of the combinations of the parameters is enormous, so the arithmetic processing amount necessary for the calculation is enormous. For example, when the seventeen parameters are included and ten values of each parameter are used in the calculation, 1017 times (=a hundred quadrillion times) of the calculation is necessary.
The problem of such the enormous arithmetic processing amount is not limited to the case of the fuel pressure sensor that senses the fuel pressure change but also occurs similarly in the cases of all the sensors that sense physical quantity changes.